Casts made of a variety of materials and thicknesses are often used to facilitate healing of injuries in human and animal patients. For example, casts may be formed of plaster or fiberglass cloth over cotton gauze. At a certain point in the healing process, the cast will be removed by a medical practitioner, often using a cast saw.
Known cast saws are evolved from cadaver saws and woodworking tools, with little change to these two designs. The first group of tools employs a blade mounted on a shaft which runs longitudinally through the tool and the location where the tool is gripped by the operator's hand, and cuts at a right angle to this shaft. The motor and most weight is aft of the hand, and the operator must move the tool left and right. The operator's wrist and thumb are used to move constantly the blade in and out of the cast material being cut.
The second group of tools has the motor located within the area gripped by the operator's hand. This provides better balance, but the diameter of the device is larger which is a problem for operators with small hands. This type of tool uses a right angle gear box to mount the blade in line with the tool body, so the cutting motion is to push the tool into the cast material. Because the tool is held free in the air, it cannot be easily controlled or stabilized on the cast, and must be moved with constant wrist motion.
Both of these tools oscillate the blade in a narrow arc of about 2.5 to 3.0 degrees and use small teeth to avoid enough motion to cut the patient should the blade come into contact with the skin. This small motion of the blade is further reduced by the reaction of the tool to the blade motion and counter-oscillation of the tool body. This means that only a few of the teeth are actually engaging the cast material on any stroke, so the stroke is less than optimum. The high oscillation speed of the tool (approximately 15,000 per minute) is translated into vibration of the tool in the operator's hand and a loud noise is produced. The blade teeth fill with dust and cease to cut, so the operator must move the blade in and out of the work constantly to put clean teeth into the cast cut. This inefficiency of the cutting motion, combined with the gear box and oscillating mechanism, requires more power yielding more heat and more noise. The power requirements are too much for many battery powered motors, so AC motors are used. AC motors are powerful, but are noisy (e.g., due to the brushes).
Overall, cast saws of the prior art are heavy and tiring to use. Many medical personnel simply cannot handle them. They are noisy to point of being detrimental to hearing, so many of them have to be used in special rooms. Their vacuum systems are also noisy, and must be isolated in closets. Example cast saws of the prior art are shown and described in U.S. Pat. No. 1,530,023, issued Mar. 17, 1925 to Walton, U.S. Pat. No. 2,490,878, issued Dec. 13, 1949 to Marsh, and U.S. Pat. No. 3,103,069, issued Sep. 10, 1963 to Gary. Each of the foregoing patents is incorporated herein by reference in its entirety for all purposes.